1. Field
Example embodiments relate to an organic electronic device including a semiconductor layer and source/drain electrodes formed from materials of the same type. Other example embodiments relate to an organic electronic device including a substrate, a gate electrode, a gate insulating layer, a semiconductor layer, and source/drain electrodes, in which the semiconductor layer and the source/drain electrodes may be formed using organic semiconductor type materials suitable for a room-temperature wet process, and thus have surface properties similar to each other, thereby decreasing contact resistance between the semiconductor layer and the source/drain electrodes.
2. Description of the Related Art
After the development of polyacetylene, which is a conjugated organic polymer having semiconductor properties, an organic semiconductor is receiving attention as a novel electric and electronic material due to the advantages of organic material, for example, various synthesis methods, easier formability into fibers or films, flexibility, conductivity, and decreased preparation costs, and thus has been studied in the field of functional electronic devices and optical devices. Of devices using such a conductive polymer, research into organic thin film transistors (OTFTs) including a semiconductor layer formed of organic material began in 1980 all over the world.
Compared to conventional silicon thin film transistors, OTFTs are advantageous because a semiconductor layer may be formed through an atmospheric pressure printing process in place of plasma-enhanced chemical vapor deposition (PECVD), and all of the fabrication processes may be carried out using a roll-to-roll process on a plastic substrate, if necessary, thus decreasing the cost of fabricating the transistor. Accordingly, the OTFT may be variously applicable to driving devices of active displays, smart cards and/or plastic chips for inventory tags.
However, the OTFT has increased contact resistance between the semiconductor layer and the source/drain electrodes, amounting to about ones to tens of MQ, and thus may not be effective for carrier injection, leading to lower charge mobility and higher operating voltage and threshold voltage than in conventional silicon thin film transistors. Adhesion between metal or metal oxide, used in the source/drain electrodes, and organic semiconductor material, used in the semiconductor layer, may be undesirable due to the different surface properties therebetween, and because the metal or metal oxide has a lower work function than the organic semiconductor material, thereby forming a Schottky barrier between the semiconductor layer and the source/drain electrodes.
Methods of surface treating the interface of the semiconductor layer and the source/drain electrodes with a self-assembled monolayer (SAM) compound have been employed. One example of such a method utilizes treating the exposed surface of source/drain electrodes with an SAM compound containing a thiol functional group, so as to increase the charge mobility of the OTFT. However, the above SAM treatment method may be disadvantageous because the procedure thereof may be complicated and may be relatively difficult to apply to a semiconductor line in practice. The metal or metal oxide having surface properties different from those of the organic semiconductor material is normally used for the electrode, and therefore inherent limitations are imposed when attempting to overcome the above problems.